The present invention is in the field of apparatuses and processes particularly adapted for use in an earth fluid well. More specifically, the present invention relates to an apparatus at the end of a well conduit for separating solids from the earth fluids flowing into the conduit, the apparatus comprises a porous mass of adhered filter material.
Hydrocarbon producing wells typically are drilled many thousands of feet into the earth in order to reach an oil or natural gas bearing strata. These strata are often structurally weak or fragile geological formations comprising particulate matter, such as sand, gravel and similar materials. Consequently, the downhole formation of the well bore can be subject to degradation and the accumulation of particulates and the migration of these particulates along with the earth fluids into the well.
It is known in the field to use well screens as filters in the downhole bore of a hydrocarbon producing well to prevent the migration of particulates, such as sand, gravel and the like, into the well conduit along with the production flow. Additionally, because the downhole bore can have irregular surfaces, the field has been motivated to develop deformable well screens that are expandable downhole to at least partially set against the surrounding formation and line the borehole. For examples, see U.S. Pat. Nos. 5,901,789 and 6,012,522 to Donnelly et al. and U.S. Pat. No. 6,457,518 to Constano-Mears et al.
Further, at the points of irregularity in the borehole where the rigid, external surface of Donnelly-type well screens does not sufficiently contact the surrounding formation, undesirable gaps and channels can be formed. To reduce or eliminate the effect such formation irregularities, the field has been motivated to develop means to fill and/or support gap forming irregularities. For example, Donnelly et al. disclose the use of resin-coated gravel as a porous fill material which is separately installed in situ as a means for filling gaps between the well bore formation and the well screen.
Because of the benefit of having a downhole well screen installed in close contact with wall of the well bore formation, it would be useful in the field to have alternative downhole expandible well screens that serve not only as a production flow filters, but also as a well bore liners that require less intervention for filling gaps between the well bore formation and the well screen.
The present invention is a downhole expandable bore liner and well screen filter assembly, particularly for use in a hydrocarbon producing well bore. The liner/filter assembly comprises a perforated tubular base-pipe overlain with a filter-cover. A set of runners (bumpers) extends the length of the outer surface of the assembly. A constriction means holds the liner/filter assembly in a compressed configuration during insertion of the assembly down the well bore. The outside diameter of the liner/filter assembly in its compressed configuration is sufficiently less than the inside diameter of the well bore to facilitate insertion of the liner/filter assembly into its downhole position. Once positioned downhole in the well bore, the constriction means is released, and the liner/filter assembly takes its expanded or uncompressed configuration to interface with the walls of the well bore. In its uncompressed configuration, the liner/filter assembly can contact and press against the walls of the well bore, which contact serves to stabilize the assembly and to center it in the downhole well bore. Additionally, the resilient and malleable nature of the filter material of the filter-cover can engage and at least partially fill and stabilize the irregularities in the formation wall.
The tubular base-pipe is perforated to allow passage of earth liquids (xe2x80x9cproduction flowxe2x80x9d) from the well bore environment external to the base-pipe into its interior, and further passage into a conduit to which the liner/filter assembly (or string of liner filter assemblies) is attached. The tubular base-pipe has a central axis, a pipe-length, and a tube wall enclosing an interior space. The interior space is disposed to be communicable with the with the fluid space of a well conduit. The tube wall has a plurality of through perforations for passing fluids. Optionally, the tubular base-pipe may be expandable as is known in the field, to provide a tube wall having a plurality of through perforations for passing fluids. For example, see the U.S. Pat. No. 5,901,789 to Donnelly et al. for how to accomplish an expandable base-pipe in the present invention. Typically, the base-pipe will include a connecting means allowing the base-pipe to be joined in series with a well conduit or to another well screen liner/filter assembly. The bottom most liner/filter assembly in a series is plugged at its bottom end.
The filter-cover covers the outer tube-surface of the base-pipe and servers to filter the earth liquids before they pass through the perforations in the tube-wall of the base-pipe. The liner/filter assembly is inserted into the well bore with the filter-cover in a compressed configuration to reduce the overall outside diameter of the assembly to facilitate the insertion process. Once the liner/filter assembly is positioned downhole in the well bore, the filter-cover is allowed to take its normal uncompressed configuration. The filter-cover may be disposed on the outer surface of the base-pipe in any of a numbers of manners practicable in the present invention by one of ordinary skill in the art. For example, the filter cover may be drawn into position over the base-pipe in the manner of a sleeve, or may be wrapped in a helictical fashion over the length of the base-pipe.
The filter-cover is made of a compressible/self-expanding filter material and has a fully compressed-thickness, an expanded-thickness, a fully compressed outer-diameter and an expanded outer-diameter. The filter-cover is made of a filter material impervious to the fluids which it is to filter. In the present invention, the filter-cover comprises a filter material which is substantially impervious to fluids containing hydrocarbons. The filter-cover may comprise one or more layers of filter material, and the different filter material layers may have different physical and/or structural characteristics. For example, the filter-cover may comprises one or more filter materials selected from the group consisting of: a fiber matrix, an open cell foam. Additionally, the different layers of filter materials may have different physical-chemical characteristics and different porosity or filtering characteristics.
Typically, the filter material will have sufficient porosity to pass earth fluids and gas, while filtering out most particulates from the production flow. An appropriate filter material for practice in the present invention in a hydrocarbon producing well is resistant to exposure to crude oil, brine and to other fluids used in producing hydrocarbon wells. Additionally, the filter materials should be resistant to the temperatures, pressure and conditions of pH that may be experienced in hydrocarbon producing wells. The filter material is also mechanically resilient and has sufficient memory to expand to substantially its initial uncompressed condition (thickness) after being bound for a time in a compressed condition. Several polyurethane open-cell foam materials have been found to meet these requirements. It is likely that other materials, such as silicone resin based open-cell foams will also meet these filter material requirements.
A set of runners extend the length of the filter-cover and protrude radially beyond the outer surface of the filter-cover when the liner/filter assembly is in its compressed configuration. The runners are disposed at the outer cover-surface of the filter-cover in a spaced relationship to each other. The space relationship of the runners extends the pipe-length of the base-pipe, and define the overall outer diameter of the liner/filter assembly in its compressed configuration. The runners act as standoffs or bumpers to prevent damage to the filter-cover during insertion of the liner/filter assembly into the well bore. Consequently, the runners are made of an abrasion resistant material such as polyurethane, high density polyurethane, a high-impact plastic, a metal or an appropriate composite material. This facilitates the insertion of the well screen several thousand feet through the abrasive conditions of a well bore without substantial damage to the filter-cover. Suitably abrasion resistant runner-material are selectable by one of skill in the art. Additional examples of suitable runner-material include resin, and fiber reinforced plastic.
The runners of the downhole expandable bore liner and well screen assembly have a substantially parallel spaced relationship to each other and to the pipe-length of the base-pipe. Alternatively, in certain applications, the runners can have a substantially parallel spaced relationship to each other, but a non-parallel relationship to the pipe-length of the base-pipe.
The constriction means holds the runners in spaced relationship to each other, while also holding the filter-cover in a compressed condition. The constriction means are disposed circumferentially around the liner/filter assembly and in a spaced pattern crossing the runners. The constriction means serve, either alone or in combination with the runners, to hold the filter-cover in a compressed configuration. The constriction means are disposed in a spaced pattern sufficient to compress the filter-cover to have an external surface with an outer-diameter at a radial distance from the base-pipe axis which is less than the radial distance of an outer edge of the runners proximate the external surface of the compressed filter-cover.
Once the liner/filter assembly is positioned downhole in the well bore, the constriction means are released. Release of the constriction means allows the filter material to expand and reassume it natural uncompressed condition. In an appropriately constructed liner/filter assembly, the filter-cover will contact the formation wall of the well bore upon resuming its substantially completely uncompressed condition. When contacting the formation wall in its uncompressed condition, the filter-cover stabilizes and tends to center the liner/filter assembly in the downhole well bore.
The constriction means is comprised of a material and disposed in the assembly in a manner to make it susceptible to release. To accomplish a releaseable constriction means several mechanisms are available. Examples include constriction means comprising a fusible link, a mechanical tie assembly, and a dissolvable link. Other releaseable constriction means are selectable by the ordinary skilled artisan.
Electro-chemical mechanisms have been utilized to release the constriction means. In one example, the constriction means comprised aluminum wire tightly wrapped around the runners and compressing the filter-cover. Release of the constricting aluminum wire was accomplished by immersing the assembly in a 10% sodium hydroxide solution and dissolving the aluminum wire. In another example, the assembly was immersed in a brine solution and a d.c. voltage was applied to the aluminum wires and to the steel base-pipe. In this example, the aluminum wires became one electrode (the anode) and the steel base-pipe became the other electrode (the cathode) and on the application of an appropriate voltage across the electrodes, the aluminum wires were dissolved in the brine solution by electrolysis.
Chemically releaseable constriction means can be accomplished by constructing the constriction means from a chemically dissolvable material. In this example, the constriction means holding the filter-cover in a compressed configuration is a plurality of dissolvable links, the links being dissolvable in an appropriate solvent or chemical agent. Once the assembly is in place, the appropriate solvent is dispersed into the downhole environment of the assembly to dissolve the constriction means. Alternatively, the solvent to which the chemically releaseable constriction means is susceptible may already be present or otherwise already available downhole. For example, the selected chemically releaseable constriction means in an appropriate situation may be susceptible to crude oil.
A fusible link type releaseable constriction means is accomplished in the present invention utilizing a fusible electrical wire in communication with an electric current source. The fusible electrical wire is tightly wrapped around the runners, compressing the filter-cover. A pair of electrodes communicate with the fusible electrical wires and provide an electrical current source through the wires. Once the liner/filter assembly in its compressed configuration is positioned downhole in the well bore, an appropriate electrical current is run through the fusible wire via the electrodes and the fusible electrical wires are severed by the current. Upon electrically severing the wire, the constriction means is defeated and the filter material resumes its uncompressed configuration. The electrodes used to carry the electrical current in this example can accomplished by making two or more of the runners out of an electrically conductive material and connecting them to a source of electricity. Using runners as electrodes has the benefit of distributing the fusing current along the entire length of the filter-cover and runners.
A mechanical type releaseable constriction means may be accomplished by a simple mechanical tie assembly in which a series of circumferential cross-ties, each cross-tie having two ends are releaseably connectable together by a removable tie-rod, are disposed along the length of the assembly. The cross-ties are released by withdrawing the tie-rod.